The present invention relates to microwave probes suitable for insertion and detection of microwave signals in high frequency circuit assemblies, and more particularly to a microwave probe which can be used with densely populated surface mount and hybrid circuit assemblies.
Generally, most modern RF microwave circuits and assemblies use planar transmission line structures such as a microstrip or a coplanar waveguide to transmit high frequency signals from one circuit or device to another. Various probe structures have been developed which facilitate xe2x80x9con-waferxe2x80x9d testing and various forms of rapid characterization of high frequency circuits, such as Microwave Integrated Circuits (MIC) and Monolithic Microwave Integrated Circuits (MMIC). One such probe is generally known as an RF wafer probe, which operates as a miniature transmission line structure to permit interfacing with a coaxial transmission line. With such a probe, RF characterization is possible for MMIC devices.
The problem with known wafer probes derives from the fact that the probe design utilizes a planar, blade-like contact element, which requires contact with the microwave circuit at a very low angle relative to the circuit board. Pressure must then be applied to the probe assembly to slightly deflect the probe contact tip to make positive contact with the RF circuit being tested. Such probes were specifically designed to test microwave devices at the flat wafer level, such as the aforementioned MMIC devices. In other words, there are virtually no structures protruding from the surface of the wafer that the probes are required to clear when brought into contact therewith.
However, many RF and microwave assemblies and units are fabricated using either surface mount technologies, or hybrid circuits formed from combinations of surface mount and integrated circuits. These technologies allow the combination of several RF circuits, such as amplifiers, mixers, oscillators, and filters, to be integrated into a planar receiver or synthesizer circuit. The circuits and components in such assemblies are typically located as close as possible to decrease overall size, weight, and cost of the circuit. Because of dense packaging of components on planar circuits, use of conventional wafer probes is either prohibited or restricted due to the requisite low contact angle. In other words, because of the low angle at which known wafer probes contact a circuit board, there are many configurations of surface mount and hybrid circuits where such a probe would not be able to contact the circuit due to the positioning of some nearby component attached to the planar circuit, or due to the type of package in which the circuit has been placed.
In addition, known wafer probes also have very limited ability to make simultaneous contact with surfaces of different heights. More specifically, most common microwave applications call for a coplanar or xe2x80x9cground-signal-groundxe2x80x9d type probe, which is used to contact a type of transmission line known as a coplanar waveguide. As shown in FIG. 1, a coplanar waveguide 10 is formed from a substrate 12 having a plurality of metal strips formed on the surface thereof. A center strip 14 provides a signal line, while side strips 16 and 18 are located on both sides of the center strip and separated by uniform gaps. Metal strips 16 and 18 connect to a ground potential of the RF system. Electromagnetic fields are supported between the center conducting strip and the strips which form the ground. Known coplanar waveguide wafer probes are limited in their ability to bridge nonuniform trace heights between the signal and ground strips.
Therefore it is an object of the present invention to provide an improved microwave probe which can be used with surface mount, and hybrid microwave circuit assemblies.
It is another object of the present invention to provide a microwave probe which can be used with microwave circuit assemblies having probe contact points of non-uniform surface height.
In accordance with these and other objects, a probe is provided for making temporary connections to a planar transmission line integrated onto a circuit board, wherein the probe includes a probe housing, a signal pin having a first end extending outwardly from the probe housing, and at least one ground pin also having a first end extending outwardly from the probe housing. The signal pin and the at least one ground pin are affixed to the probe housing with an orientation relative to each other to permit contact with the planar transmission line when the signal pin and the ground pin(s) are substantially perpendicular to the transmission line.
In accordance with one aspect of the present invention, each pin on the probe is individually spring-loaded to allow simultaneous contact of the probe with a transmission line or circuit board having a non-uniform surface height.
Thus, the probe of the present invention allows contact with a wide variety of planar transmission line circuits so that the probe pins are substantially perpendicular to the surface of the circuits. As a result, minimal surface area clearance is required, thereby permitting use of the probe in close proximity to any nearby component, circuit, or circuit package. Therefore, the present invention overcomes the difficulties of known wafer probes and allows individual circuit functions to be characterized or tested in situ on surface mount or hybrid circuit assemblies. This, in turn, allows test access to surface mount and hybrid circuit assemblies without concern of packaging density.
The above objects and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.